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TnSlim · Joined: 08 Sep 2003 Posts: 355 Location: Curaçao, N.A.

I put new Bridgestone RE960AS Pole Positions on my ’97 328I. Although they were the same size as the tires they replaced, I could tell the new sneakers were quite a bit taller by comparing the relationship of the tach to the speedo when in 5th gear. The best fuel economy I’d ever recorded on it had been 28 mpg. With the first full tank on the Interstate with the new tires, I got 33mpg, a 17% increase. The difference hasn’t been as dramatic during …ahem …spirited driving but, then again, with new rubber, I’m pushing it all the harder.

Has anyone else seen such a dramatic boost in economy come from changing tires?

panzerkeil302 · Joined: 10 Mar 2004 Posts: 2182

Sports Car Revolution (on speed channel) put new tires on a project car and lost 15hp - the outer radius had increased, which decreased rear wheel HP.

Any decrease in rotational mass will have a dramatic effect on hp and your overall mpg...undersized drive pullies, lighter rims, aluminum drive shaft.

not only will oversized tires and rims decrease hp, they increase your braking distance...not my cup of tea, unless they are the spinny type that keep turning when you're at a stop light.